Enter humans, exit prehistoric carnivores

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LOS ANGELES, July 6 (UPI) -- The extinction of woolly mammoths and other large prehistoric mammals may have been aided by adding one more predator -- humans, U.S. researchers discovered.

Scientists said the mass extinction was caused by newly arrived humans who tipped the balance of power while competing with major predators such as sabertooth tigers, the authors said in their article published in the July 1 edition of BioScience. The disruption, the article said, could explain the loss of two-thirds of North America's large mammals about 15,000 years ago.

"We suggest that the arrival of humans to North America triggered a trophic cascade in which competition for the largest prey was intensified, ultimately causing the large non-human carnivores to decimate the large herbivores," said Blaire Van Valkenburgh, University of California-Los Angeles professor of ecology and evolutionary biology and a co-author on the paper. "When human hunters arrived on the scene, they provided new competition with these carnivores for the same prey."

Adding the human element was different from the arrival of other predators because humans were omnivores and could live on plants if necessary, Van Valkenburgh said.

"We think this may have triggered a sequential collapse not only in the large herbivores, but ultimately their predators as well," she said. "Importantly, humans had some other defenses against predation, such as fire, weapons and living in groups, so they were able to survive."

The loss of species in North America during the late Pleistocene was remarkable, researchers said. About 80 percent of 51 large herbivore species went extinct, along with more than 60 percent of large carnivores.